Field of the Invention
The present invention relates generally to methods and systems for lifting and manipulating loads. More particularly, but not by way of limitation, the present invention relates to methods and systems for utilizing a gantry crane and rail system to safely lift more than a rated capacity of the gantry crane.
History of the Related Art
Cranes are frequently used in activities such as, for example, construction, manufacturing, mining, and refining to lift and manipulate heavy objects. In particular, gantry cranes, bridge cranes, and overhead cranes are examples of cranes that lift objects via, for example, a hoist secured to a hoist trolley. The hoist trolley moves along a rail or pair of rails that are affixed to a beam. In overhead cranes and bridge cranes, ends of the beam include wheels that engage rails. The beam typically traverses a working space such as, for example, an interior of a factory or similar industrial building. In contrast, the beam of a gantry crane is supported by one or more upright support gantries. The support gantries are often mounted on wheels thereby allowing the gantry crane to traverse a working area such as, for example, a rail yard or a dry dock. In cases where the loads to be lifted are easily moved, such as, for example, in a rail yard, the support gantries may be fixed to the ground.
All cranes, and particularly gantry cranes, are designed with a maximum-safe-load capacity. Exceeding the maximum-safe-load capacity carries risk of damage to the cranes and the surrounding structures as well as risk of personal injury and loss of insurance coverage. However, in large projects such as, for example, construction, mining, and refining it is often necessary to lift loads exceeding the maximum-safe-load capacity of an available gantry crane. In such situations, gantry cranes are often supplemented with one or more mobile cranes to increase an effective maximum-safe-load capacity. However, use of mobile cranes typically requires construction of a suitable foundation. Furthermore, space constraints in an area surrounding a construction site, a mine, or a refinery often render the use of mobile cranes infeasible.